Add a What's New entry for Emscripten (GH-137035)

(cherry picked from commit d7e12a3)

Co-authored-by: Hood Chatham <[email protected]>
Co-authored-by: Adam Turner <[email protected]>
Co-authored-by: Hugo van Kemenade <[email protected]>
Co-authored-by: Stan Ulbrych <[email protected]>

Author: 4 people

Doc/whatsnew/3.14.rst

@@ -1081,6 +1081,18 @@ The behavior of :func:`!gc.collect` changes slightly:
 
 (Contributed by Mark Shannon in :gh:`108362`.)
 
+Platform support
+================
+
+* :pep:`776`: Emscripten is now an officially supported platform at
+  :pep:`tier 3 <11#tier-3>`. As a part of this effort, more than 25 bugs in
+  `Emscripten libc`__ were fixed. Emscripten now includes support
+  for :mod:`ctypes`, :mod:`termios`, and :mod:`fcntl`, as well as
+  experimental support for :ref:`PyREPL <tut-interactive>`.
+
+  (Contributed by R. Hood Chatham in :gh:`127146`, :gh:`127683`, and :gh:`136931`.)
+
+  __ https://emscripten.org/docs/porting/emscripten-runtime-environment.html
 
 Other language changes
 ======================